Abstract
Investigation of the Red Sea sponge Negombata magnifica gave two novel alkaloids, magnificines A and B (1 and 2) and a new beta-ionone derivative, (+/-)-negombaionone (3), together with the known latrunculin B (4) and 16-epi-latrunculin B (5). The analysis of the NMR and HRESIMS spectra supported the planar structures and the relative configurations of the compounds. The absolute configurations of magnificines A and B were determined by the analysis of the predicted and experimental ECD spectra. Magnificines A and B possess a previously unreported tetrahydrooxazolo[3,2-a]azepine-2,5(3H,6H)-dione backbone and represent the first natural compounds in this class. (+/-)-Negombaionone is the first beta-ionone of a sponge origin. Compounds 1-3 displayed selective activity against Escherichia coli in a disk diffusion assay with inhibition zones up to 22 mm at a concentration of 50 mu g/disc and with MIC values down to 8.0 mu M. Latrunculin B and 16-epi-latrunculin B inhibited the growth of HeLa cells with IC50 values down to 1.4 mu M.